1. Field of the Invention
This invention relates to a drive device, especially for displacement of the sliding roof of a motor vehicle, with an electric motor which has a pole shaft located in a shaft housing, and a magnet which is located on the pole shaft so as to rotate with the shaft, and at least one Hall sensor which is located outside of the shaft housing for detecting the rotational position of the magnet and thus of the pole shaft.
2. Description of Related Art
A drive device of the initially mentioned type is described in published German Patent Application DE-OS 44 20 692. Here, an electric drive motor and a worm gear pair which is coupled to the driven shaft of the motor are accommodated in a housing. In order to detect the rotational position of the driven shaft, a magnet is located on the driven shaft so as to rotate with it, and outside of the housing in which the driven shaft is located, there are Hall sensors on which pulses are produced upon rotary motion of the magnet in order in this way to detect the rotational position of the magnet, and thus, of the driven shaft. According to one embodiment of German Patent Application DE-OS 44 20 692, the Hall sensors are enclosed in their own housing which is then placed on the housing of the driven shaft. According to another embodiment, the Hall sensors are located on a carrier plate which is connected from the outside to the housing of the driven shaft so that, in this case, the carrier plate and the Hall sensors are freely accessible from the outside and are thus unprotected.
In both cases, the motor is triggered and the pulses which have been detected by the Hall sensors are evaluated in a control unit which is located at a distance from the drive device and which is not explained in detail in application DE-OS 44 20 692.
U.S. Pat. No. 6,162,142 discloses a drive device for a motor vehicle roof in which rotation of the driven shaft of the electric motor is tapped by means of a worm gear pair which is held in contact with the driven shaft by means of a housing which surrounds both the driven shaft and the worm gear pair. Furthermore, the housing has a housing area which is laterally offset next to the worm gear pair and in which there is a board on which there are components for triggering the drive motor and Hall sensors for detecting the rotational position of the driven shaft. The individual assemblies, especially the driven shaft and the worm gear pair which is driven by the driven shaft, are not shielded relative to the board so that there is the danger that the lubricant which is ordinarily provided between the driven shaft and the worm gear pair can leak onto the board and the components located on it; this can lead to an adverse effect on the function of these components and the Hall sensors.
Additionally, U.S. Pat. No. 5,768,942 discloses a drive for a motor vehicle roof in which the reducing gear and electrical circuit are accommodated in separate housing parts which are detachably joined to one another to enable flexible matching to different circuit layouts. The gear housing part is produced as a metal die casting and the electric housing part as an injection molded plastic part.